The invention relates to a developer mixture which is suitable for developing negative-working exposed reproduction layers in copying materials, to a process for preparing printing forms, and to the use of the developer.
Copying materials of the stated kind are used in particular in the preparation of printing plates or photoresists and comprise a base and a negative-working light-sensitive reproduction layer. The bases used in these copying materials are metals such as zinc, chromium, copper, brass, steel, aluminum or combinations of these metals, plastic films, paper or similar materials. These bases can be coated with the light-sensitive reproduction layer without a modifying pretreatment, but preferably are first subjected to a surface modification such as a mechanical, chemical or electrochemical roughening, an oxidation and/or a treatment with hydrophilizing agents (for example in the case of offset printing plate bases). The reproduction layers to be developed according to the invention contain water-insoluble diazonium salt polycondensation products. In addition to the light-sensitive component, the reproduction layers can also contain plasticizers, pigments, dyes, wetting agents, sensitizers, indicators and other customary additives. Such reproduction layers are exhaustively described for example in U.S. Pat. No. 3,867,147.
A developer for negative-working reproduction layers must be able to dissolve those parts of the layer which have not been exposed to electromagnetic radiation (the latent nonimage areas) out of the exposed layer without significantly affecting those parts of the layer which have been exposed to the radiation (the latent image areas). Electromagnetic radiation can be, for example, visible light. The above-cited patent mentions as generally suitable developers: water, water/organic solvent mixtures, aqueous salt solutions, aqueous acid solutions, aqueous-alkaline solutions and undiluted organic solvents, to which surfactants and/or hydrophilizing agents may be added. The developers chiefly used in the examples contain water, sodium lauryl sulfate, sodium sulfate, tartaric acid and in some cases benzyl alcohol; other developers contain or comprise isopropanol, n-propanol, n-propyl acetate, polyacrylic acid, 1,1,1-trichloroethane, acetone or ethylene glycol monomethyl ether.
The prior art additionally discloses the following developers and developer mixtures:
German Auslegeschrift No. 1,047,016 describes the addition of 3 to 5% by weight of propylene oxide/ethylene oxide block polymers having terminal ethylene oxide units to an aqueous developer which contains phosphoric acid and is used for light-sensitive colloid layers which are on planographic printing plates and contain diazonium compounds.
The aqueous, alkaline developers of U.S. Pat. No. 3,201,241 for negative layers on planographic printing plates contain 0.3 to 5% of alkali, 0.001 to 0.05% of certain cations such as Ca.sup.2+, Sr.sup.2+, or Ba.sup.2+, 0.001 to 0.25% by weight of complexing agents such as tartaric acid, ascorbic acid or ethylenediaminetetraacetic acid and 0.2 to 0.8% by weight of water-soluble polymers such as polyethylene glycols or cellulose ethers. If the negative layers which contain p-quinonediazides as the light-sensitive compound also contain binders, the developer generally has added to it also organic solvents such as ethylene glycol monomethyl ether.
U.S. Pat. No. 3,701,657 discloses a non-aqueous developer, for planographic printing plates with a photopolymerizable resin, which contains an organic solvent, a low-molecular surfactant and if desired, as hydrophilizing agent, a low-molecular acid such as citric acid or phosphoric acid or a hydrophilic colloid such as carboxymethylcellulose. Surfactants which are mentioned as suitable are, inter alia, alkylarylsulfonic acids and polycondensation products of ethylene oxide and alcohols, fatty alcohols, alkylphenols or fatty amines.
The developer for negative layers as described in U.S. Pat. No. 3,669,660 contains water and a water-soluble sulfonic acid (in particular aromatic compounds) or one of its water-soluble salts and if desired a water-soluble organic solvent, a surfactant and an acid such as phosphoric acid. The light-sensitive layers to be developed are said to be based on p-diazodiphyenylamine. The developer contains the sulfonic acid compound in a proportion of 5 to 25% by weight, the organic solvent in a proportion of 0 to 20% by weight, up to 5% by weight of the surfactant (for example sodium lauryl sulfate) and up to 5% by weight of the acid.
U.S. Pat. No. 4,147,545 describes a developer for negative layers which contains a water-soluble lithium salt of an organic compound with at least one acidic hydrogen atom and if desired an amphoteric surfactant. Suitable lithium salts include, inter alia, lithium-dodecanoate, -lauryl sulfonate, -chloroacetate, -caprylate, -stearate and -oleate, and they are added to the aqueous solution in a proportion of 1 to 25% by weight. The amphoteric surfactant can be present in the developer in a proportion of up to 50% by weight. The developer can in addition contain up to 30% by weight of an organic solvent, up to about 10% by weight of an nonionic surface-active agent and up to 5% by weight of phosphoric acid or oxalic acid. The light-sensitive layer to be developed is based on water-insoluble diazonium compounds or on photo-polymerizable compounds.
The amphoteric surfactants contain not only a grouping having a basic nitrogen atom but also a grouping having an acid function, such as a carboxyl, sulfate, sulfonate or phosphate radical. A further addition can also comprise ionic or nonionic surfactants in a proportion of 5 to 10% by weight. Those mentioned include, inter alia, polyethylene glycol ethers of alcohols or alkylphenols.
The developer which is described in British Patent No. 1,515,174 for treating negative layers containing diazonium salt polycondensation products contains a major proportion of water, a smaller amount of an organic solvent and a water-soluble colloid. Such a developer can also contain up to 10% by weight of a surfactant and up to 20% by weight of a salt or an acid (inter alia sulfates, phosphates, nitric acid, phosphoric acid); surfactants mentioned as suitable are, inter alia, sodium lauryl sulfate, alkyl polyethylene glycol ethers and alkylphenol polyethylene glycol ethers.
U.S. Pat. No. 4,186,006 discloses a developer, for light-sensitive layers containing a water-insoluble diazo resin and a hydrophobic resin, which contains (a) benzyl alcohol, ethylene glycol monophenyl ether or monobenzyl ether, (b) an anionic surfactant and (c) a water-soluble sulfite.
European Patent Application No. 0,056,138 discloses a process and a developer mixture for developing exposed negative-working diazonium salt layers which is composed of water, a salt of an alkanoic acid and a nonionic surfactant. In the mixture, the stated constituents are said to be in a specified ratio to each other.
European Pat. No. 0,033,232 describes a process for developing an imagewise-exposed, negative-working planographic printing from material with an essentially aqueous developer which contains a nonionic surfactant and additionally a salt of an aliphatic carboxylic acid having up to 9 carbon atoms.
European Patent Application No. 0,080,042 concerns a developer for removing the unexposed areas of light-sensitive coatings which contain a high-molecular polymer. The developer contains a surface-active agent, organic solvent, an alkaline agent, for example alkaline salts, amines or imines, and 0.01 to 5.0% by weight of a water-softening agent.
British Pat. No. 2,110,401 discloses a developer which comprises a water-miscible solvent for the binder and water and a mixture of a hydrophilic anionic surface-active agent and an organophilic nonionic surface-active agent.
European Pat. No. 0,004,014 discloses a developer solution which is intended for developing exposed light-sensitive copying layers containing a diazonium salt polycondensation product and a water-insoluble organic polymer, which comprises a buffered aqueous solution of a water-soluble polymer, an anionic wetting agent and a water-miscible organic solvent. The solution has a pH of from 3 to 9, and contains 0.5 to 15% by weight of anionic wetting agent as the water-soluble polymer, 0.5 to 6% by weight of poly-N-vinyl-methylacetamide or 1 to 5% by weight of polyvinyl alcohol, 0.5 to 6% by weight of a salt or salt mixture which stabilizes the pH within the indicated range, from 0.5% by weight to saturation concentration of benzyl alcohol and from 0.5% by weight to a saturation concentration of glycerol triacetate.
German Offenlegungsschrift No. 2,941,960 describes a developer mixture which is intended for washing away imagewise-exposed light-sensitive copying layers containing a polymer of an N-vinylamine, vinyl alcohol or a vinyl alcohol derivative, an alcohol which is soluble in water to less than 10% by weight, and water as the main component. The mixture comprises a copolymer which is water-soluble, or dispersible in water to form a stable dispersion, from
(a) hydrophilic units of the formula I ##STR1## in which A denotes ##STR2## R denotes a hydrogen atom or a methyl group, R.sub.1 denotes a hydrogen atom, an alkyl group or an alkoxyalkyl group each having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms, PA0 (b) hydrophobic units of vinyl monomers, whose homopolymer is water-insoluble and which have as a substituent an aromatic or a long-chain aliphatic radical, the proportion of hydrophobic units being sufficiently high that a 0.1% strength solution of the copolymer has a surface tension of no more than 50 mN/m. The amount of copolymer is at least sufficient to emulsify any alcohol present in excess of the solubility limit.
R.sub.2 denotes an alkyl group or an acyl group each having 1 to 5 carbon atoms,
and where a homopolymer of the hydrophilic units is water soluble and
However, the developers or developer mixture disclosed by the cited state of the art have in particular the following disadvantages:
They frequently contain higher proportions of organic solvents which, for ecological reasons (low-boiling, flammable, unpleasant odor, adverse effect on waste water and exhaust air, expensive precautions for removing the solvent after the developing), should ideally no longer be present in up-to-date developers.
It is true that lauryl sulfate, heretofore frequently used in practice, or other alkanesulfates or alkanesulfonates as such, are active developer components for the indicated light-sensitive reproduction layers, but they require a relatively long development time, they give rise to excessive foaming in processing machines, in particular in the case of vertical development, and the solubility at low temperatures (for example from about 10.degree. C. and lower) in water drops to such an extent that fall or winter temperatures can give rise in the stock solutions to flaky residues which are frequently troublesome to the converters. Grease spots and adhesive residues of the type which can arise in the handling of offset printing plates under practical conditions are removed by these developer components if at all only after a long treatment time and by means of additional mechanical aids.
It is true that they are indeed suitable for use for the specific reproduction layers for which they were developed and for which they have indeed been successfully used in the respective examples, but in the case of layers other than these specific reproduction layers they exhibit more or less sizeable problems; i.e. they are not universally applicable.
They are not suitable for generally suppressing the impurities (specks and fibrils) which arise in many cases, chiefly in the case of automatic development, as redeposits on the printing forms, so that it is impossible to obtain quality end products, even on prolonged use of the developer.